Method of treating impregnated insulation



FRED L. DAMARIN, OF VILLA PARK, AND DONALD A. HARPER, OF CHICAGO, ILLINOIS, ASSIGNORS TO BROWN & OAINE (CHXCAGO DIVISION) OF TUNG-SOL LAMP WORKSZ mo, OF CHICAGO, ILLINOIS, A CORPORATION OE DELAWARE METHOD OF TREATING IMPREGNATE INSULATION Ho Drawing.

Cur invention relates to the method of improving the electrical characteristics of impregnated porous insulation by treatment with hot oil, and has for its principal object the provision of a new and improved method whereby insulation can be treated in hot oil without lowering its dielectric constant.

In our copending application, Serial No. 414,583, filed Dec. 16, 1929, We disclosed a method of treating paper or other porous insulating material, such as is used in condensers, electrical coils and the like. This method comprises impregnating the paper with a wax-like compound such as hexa-chlorinated naphthaline, commercially known as halowaX, parafiin, or other similar substance, the impregnation taking place under vacuum and at asufficiently high temperature to completely withdraw the water from the device.

After the impregnation has been completed, the device is allowed to cool to normal room temperature and then immersed in a bath of hot oil the temperature of which is slightly below the melting point of the impregnating medium. The oil is preferably a highly refined mineral oil, such as, for example, petrolatum, or a mixture of such oil and a vegetable oil. The device is allowed to soak in this hot oil long enough to insure that the impregnating medium will absorb all of the oil that it is possible for it to absorb, and to insure that all of the voids and interstices will be filled with oil.

This method of treating the wax impregnated porous insulating material improves the characteristics of that material over a similar material that is impregnated only in wax. However, in the case of paper insulation for a condenser, the absorption of oil in the wax-like impregnating compound lowers the dielectric constant of the compoundand necessitates that the plate area of the con- ,denser be. increased to compensate for the lowered overall dielectric constant of the device. For example, in a'certain embodiment.-

of this process, the impregnating medium has a dielectric constant of 4, the oil used to oil impregnate the device has a dielectric constant of 2, and the resultant device has a application filed December 16, 1929. Serial No. 414,584.

. upon the process of our above mentioned copending application, the improvement permitting us to saturate the wax-like impregnating material with oil without materially lowering its dielectric constant so that the finished condenser, for example, has

the same, or substantially the same dielectric constant as a similar wax-impregnating condenser that has not been oil treated.

The method of carrying out our improved process follows closely the method outlined in our above mentione'd'copending application. The electrical units are dried and impregnatedunder vacuum at a temperature sufliciently high to insure complete removal of moisture from the unit. This impregnation iscarried on for a suflicient interval of time to insure that the porous insulation, usually paper, will be completely saturated with the wax-like impregnating medium. The unit is then removed from the impregnating bath, drained, and allowed to cool down to the normal temperature of about 70 F.

The oil into which the condenser is to be subsequently immersed is prepared in a spe-' cial manner. This preparation consists of heating the oil to a temperature in excess of the melting point of the impregnating compound used to saturate the insulation of the wax is dissolved in it in sufiicient quantity to make a completely saturated solution. This saturated solution is then lowered to a temperature slightly below the melting point of the halowax.

The cooler oil is then a supersaturated solution of oil and halowax and has a considerable amount of halowax held in suspension in the oil. The solution is very unstable at this lowered temperature. We have found that the best working tem perature for the supersaturated solution is from 10 to 15 below the meltingpoint of the impregnating compound, which, in case of halowax, brings the working temperature down to about 200 F. I x

The cooled unit, such as condensers, that are at room temperature of are then immersed in the supersaturated solution of .oil and wax, the entrance of more wax into the oil causing the suspended particles of wax to crystallize and fall to the bottom of the vat containing the solution. The immersing of a cold device in a hot bath expands the device forming a vacuum therein which causes the oil-wax solution to be drawn into the device to completely fill the voids in it.

The device is allowed to remain in the supersaturated solution sufliciently long to insure that the wax with which it is impregnated, will absorb all of the oil that it possibly can. We allow the oil bath and device to cool to room temperature before the device is removed and find that this procedure reduces wax strains in the device. The-absorption of oil by the wax surrounds the crystals of that wax with oil, thereby giving greater elasticity to the impregnated device and consequently increasing its life when it is 0perated on alternating currents or pulsating direct current.

As is well understood by those skilled in the art, a condenser expands siigthly when it absorbs acharge and contracts when that charge is withdrawn from it. This is purely a mechanical motion and in time will cause further crystallization of theimpregnating wax as well as further crystallization of the somewhat porous insulating material, such as paper, with which the unit is insulated. The result of this further crystallization is an eventual breakdown of insulation and short circuit of the condenser which, of course, ruins it as an electrical condenser.

We have found that condensers which are impregnated in the foregoing manner are better able to withstand high voltages of alternating current and direct pulsating current because. of the presence of oil between the crystals in the impregnating wax. We have also found that because the oil is saturated with wax, the entrance of the solution of wax and oil into the impregnating wax of the unit does not materially lower the dielectric constant of the unit.

We have also found that in a specific em bodiment of our invention, a condenser impregnated with wax which has a dielectric constant of 4 and with an oil which in its natural state has a dielectric constant of 2, with that oil saturated with the wax prior to the immersion of the unit in it, the dielectric constant of the completed unit is substantially 4, rather than 3 as was the dielectric constant of the unit impregnated in raw oil. In certain instances the dielectric constant of the finished article was as high as 3.95, some variation from that being expected.

The improved method of impregnating the electrical unit, particularly condensers, therefore results in a unit which is improved by lubrication of the crystals so that it is more flexible and destructive crystallization of its insulation is delayed; it is completely moisture proof so that the device will remain constant under adverse humidity conditions, and all of these improvements have been achieved without lowering the dielectric constant of the insulation and without consequent necessity of increasing the surface area of the plate to compensate for this lowered constant.

Throughout this specification we have referred to the device as a condenser, that refence being made for convenience'sake only as it will be appreciated that the process of impregnation herein disclosed can be applied to other electrical devices, such as coils, and to many other devices that are now impregnated with wax or parafiin.

While we have disclosed a particular embodiment of our invention, we have done so by way of example only as there are many modifications and adaptations which can be made by one skilled in the art without departing from the scope of the invention. The various constants, such as temperature,

enumerated herein, have been enumerated Having thus complied with the statutes and described a preferred embodiment of our invention, what we consider new and desire to have protected by Letters Patent is pointed out in the appended claims What we claim is: a

1. The method of preparing an impregnating oil for impregnating wax filled insulation which comprises raising the temperature of the oil above the temperature at which the impregnation is to be made, saturating the heated oil with the kind of wax with which the insulation is filled, lowering the temperature of the oil to the working temperature to .produce an unstable supersaturated solution, immersing the wax filled body in that solution, and reducing the temperature of the solution and body to room temperature.

2. The method of preparing an impregnating oil for impregnating wax filled insulation which comprises raising the temperature ofthe oil from 50 F. to 100 F. above the temperature at which the impregnation is to be made, saturating the heated oil with the kind of wax with which the insulation is filled, lowering the temperature of the oil to the working temperature to produce an unstable supersaturated solution, immersing the wax filled body in that solution, and reducing the temperature of the solution and body to room temperature.

3. The method of preparing an impregnatin g oil for impregnating wax filled insulation which comprises raising the temperature of the oil above the temperature at which the impregnation is to be made, saturating the heated oil with the kind of wax with which the insulation is filled, lowering the temperature of the oil to from room temperature to 10 F. below the melting point of said wax to produce an unstable supersaturated solution, immersing the wax filled body in that solution, and reducing the temperature of the solution and body to room temperature.

4. The method of preparing an impregnating oil for impregnating wax filled insulation which comprises raising the temperature of the oil to from-50 F. to 100 F. above the temperature at which the impregnation is to be made, saturating the heated oil with the kind of wax with which the insulation is filled, lowering the temperature of the oil to from room temperature to 10 F. below the melting point of said wax to produce an unstable supersaturated solution, immersing the wax filled body in that solution, and reducing the temperature of the solution and body to room temperature.

5. The method of preparing an impregnating oil for impregnating wax filled insulation which comprises raising the temperature of a mineraloil above the temperature at which the impregnation is to be made, satu-' rating the heated oil with the kind of wax with which the insulation is filled. lowering the temperature of the oil to working temperature to produce an unstable supersatu rated solution, immersing the wax filled body in that solution, and reducing the temperature of the solution and body to room temperature.

6. The method of preparingan impregnating oil for impregnating wax filled insulation 1 which comprises raising the temperature of a mixture of mineral and vegetable oils above the temperature at which the impregnation,

is to be made, saturating the heated oil with the kind of wax with which the insulation is filled, lowering the temperature of the oil to the working temperature to produce an unstable supersaturated solution, immersing the wax filled body in that solution, and reducing the temperature of the solution and body to room temperature.

7. The method of treating fibrous insulation which includes the following steps, viz., drying the insulation, impregnating it in wax at a temperature above the boiling point of water, removing and draining the insulation and cooling it to room temperature, heating a mixture of oils to a temperature above the melting point of the impregnating wax, saturating the oil with impregnating wax at that temperature, cooling the saturated solution to a temperature slightly below the melting point of the wax, immersing the cool insulation in the solution, and further cooling the solution and insulation to room temperature.

8. The method of treating fibrous insulation which includes the following steps, viz., drying the insulation, impregnating it in hexa-chlorinated naphtha under Vacuum at a temperature above the boiling point of water, removing and draining the insulation and cooling it to room temperature, heating a mixture of oils to a temperature above the melting point of the impregnating wax, saturating the oil with impregnating wax at that temperature, cooling the saturated solution to a temperature slightly below the melting point of the wax, immersing the cool insulation in the solution, and further cooling the solution and insulation to room temperature.

9. The method of treating fibrous insulation which includes the following steps, viz., drying the insulation, impregnating it in wax at a temperature above the boiling point of water, removing and draining the insulation and cooling it to room temperature, heating a mixture of oils to a temperature above the melting point or" the impregnating wax, saturating the oil with impregnating wax at that temperature, cooling the saturated solution to atemperature slightly below the melting point of the wax, impregnating the insulation in the solution under vacuum, immersing the cool insulation in the solution, and further cooling the solution and insulation to room temperature.

10. The method of treating fibrous insulation which includes the following steps, viz.,

drying the insulation, impregnating it in wax melting point of the impregnating wax, saturating the oil with impregnating wax at that temperature,'cooling the saturated solution to a temperature slightly below the melttherein for a predetermined time and' cooling ing point of the wax, impregnating the insulation in the solution under vacuum for a definite time, and further cooling the soluthe solution and insulation to room temperature during the soaking period.

In witness whereof, we hereunto subscribe tion and insulation to room temperature our names this thirteenth day of December,

during that time.

11. The method of treating fibrous insulation which includes the following steps, viz., drying the insulation, impregnating it in wax at a temperature above the boiling point of water, removing and draining the insulation and cooling it to room temperature, heating a mixture of oils to a temperature above the melting point of the impregnating wax,

saturating the oil with impregnating wax at that temperature, cooling the saturated solution to a temperature between room temperature and 10 F. below the melting point of wax, immersing the cool insulation in the solution and further cooling the solution and insulation to room temperature.

12. The method of treating fibrous insulation which includes the following steps, viz., drying the insulation, impregnating it in wax at a temperature above the boiling point of water, removing and draining the insulation and cooling it to room temperature, heating a mixture of oils to a temperature above the melting point of the impregnating wax, saturating theoil with impregnating wax, at that temperature, cooling the saturated solution to a temperature slightly below the melting point of the wax, immersing the cool insulation in the solution, further cooling the solution and insulation to room temperature and removing the insulation from the solution and draining the surplussolution from it.

13. Themethod of treating wax impregmated fibrous insulation which has been impregnated in vacuum and cooled to room temperature which comprises preparing an impregnating oil by saturating it with impregnating wax at a temperature in excess of the melting point of that wax, cooling the ,saturated oil to a temperature below the melting point of the wax to secure a supersaturated solution having some wax in suspension, immersing the wax impregnated insulation in the supersaturated solution and allowing it to soak therein for a definite period of time.

14. The method of treating wax impregnated insulation which has been impregnated in vacuum and cooled to room temperature which comprises preparing an impregnating oil by saturating it with impregnating wax at a temperature in excess of the melting point of that Wax, cooling the saturated oil to a temperature below the melting point of the wax to secure a supersaturated solution having some wax in suspension, immersing the wax impregnated insulation in the supersaturated solution and allowing it to soak FRED L. DAMARIN. DONALD A. HARPER. 

